The present invention relates to methods and compositions of treating a subterranean formation with an optimized treatment fluid comprising a brine base fluid and an anionic carboxylated polysaccharide.
Subterranean wells (such as hydrocarbon producing wells and water wells) are often stimulated by hydraulic fracturing treatments. In hydraulic fracturing treatments, a viscous fracturing fluid, which may also function as a carrier fluid to carry particulates, is pumped into a portion of a subterranean formation at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed. Typically, particulate solids, such as graded sand, are suspended in a portion of the fracturing fluid or another fluid and then deposited into the fractures. These particulate solids, known as “proppant particulates” or simply “proppant,” serve to prevent the fractures from fully closing once the hydraulic pressure is removed. By keeping the fracture from fully closing, the proppant aids in forming conductive paths through which fluids may flow.
Fracturing fluids are often aqueous based fluids, which are viscosified using gelling agents (e.g., polymers) or gelling agents in combination with crosslinking agents. Often, crosslinking agents are very sensitive to the pH of the fluid and the viscosity may rise or fall dependent on the pH. While care is taken to control the fluid pH, it may be affected by the conditions of the subterranean formation. For example, the presence of soluble or partially soluble metal ions in the formation may result in considerable pH changes in the fracturing fluid. As such, the performance of the fracturing fluid may be significantly affected, resulting in, for example, the premature settling of the proppant particulates out of the fracturing fluid. Premature settling of the proppant particulates may result in fracture closure or partial closure after hydraulic pressure is removed, thereby reducing the production potential of the formation. Additionally, the fracturing fluid may be impacted fluid loss from the fracturing fluid into undesirable locations within the subterranean formation. Such fluid loss may be controlled in order to produce an effective fracturing fluid. Fluid loss control is often controlled by the gelling agents and/or crosslinking agents used to viscosify the fluid or by adding particulate solids to the fluid for the purpose of closing pore throats or other avenues for fluid loss.
Thus, fracturing fluid design can be very complex, and fracturing fluids are often designed for narrow sets of reservoir and/or pumping constraints. The complexity is further exacerbated because the availability of vast quantities of fresh water for subterranean formation operations has recently become substantially reduced both for environmental and political reasons. As a result, fracturing operations are preferably performed with sources of water such as seawater, produced water from a formation, or reclaimed water. These water sources, however, do not possess the predictable chemistry that fresh water possesses and typically contains high salt concentrations of diverse ions, often in a concentration of greater than 30,000 parts per million (“ppm”) or even greater than 200,000 ppm. This “high salt concentration water” or “high salt concentration fluid” has historically been less effective as a stable fracturing fluid capable of relatively uniformly suspending proppant particulates for delivery into a fracture, largely because gelling agents and/or crosslinking agents may be salted out of the high salt concentration fluid. Therefore, an effective fracturing fluid having a high salt concentration base fluid that may be used in subterranean formation operations may be of benefit to one of ordinary skill in the art.